The purposes of this project were to find optimal methods of assessing physical activity energy expenditure (PAEE) in a free-living condition and to use these methods to determine the impacts of physical activity frequency, duration, and intensity on health, with particular emphasis on physical activity during pregnancy. We previously collected data, using a variety of accelerometers, heart rate monitors, and pedometers, with which we proposed to estimate PAEE in a cohort of healthy young adults. We simultaneously collected laboratory, nutrition, and anthropometric data from the same cohort. No further work on this project is planned, and the project is inactivated.